Radio telephone with automatically tuned loaded antenna



April 30, 1968 J- L. GRAY RADIO TELEPHONE WITH AUTOMATICALLY TUNEDLOADED ANTENNA 5 Sheets-Sheet 1 Filed June 12, 19

VARIABLE TUNING REACTANCE MOTOR RESONANCE I RECEIVER DETECTOR MATCHINGa.

SWITCHING y as AMPLIFIER PROGRAMMER .20 FIG. 2 To ANTENNA INDICATOR TOAMP INPUT INVENTOR. JOHN L. GRAY ATTORNEYS J. GRAY 3,

RADIO TELEPHONE WITH AUTOMATICALLY TUNED LOADED ANTENNA April 30, 1968 5Sheets-Sheet Filed June 12, 1964 RE INPUT FIG. 2A

INVENTOR.

JOHN L. GRAY ATTORNEYS April 30, 1968 J. L. GRAY 3,381,222

RADIO TELEPHONE WITH AUTOMATICALLY TUNED LOADED ANTENNA Filed June 12,1964 3 Sheets-Sheet 5 4o REMOTE 1 FERRITE ROD RE INPUT TO EQ'QE INDI AM4% [LIMIT SWITCH RESONANCE b r ASSEMBLY DETECTOR I64" 224; E-LQGO 204-L9Gb 3 250 94,. 2o4

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JOHN L. GRAY ATTORNEYS United States Patent 3,381,222 RADIO TELEPHONEWITH AUTOMATICALLY TUNED LOADED ANTENNA John L. Gray, 99 Oenoke Lane,New Canaan, Conn. 06840 Filed June 12, 1964, Ser. No. 374,765 12 Claims.(Cl. 32525) ABSTRACT OF THE DISCLOSURE An apparatus for automaticallyself-tuning a loaded antenna with a sensor coupled to the antennacircuit for sensing when the antenna is tuned for resonance to an RFsignal source. A logic circuit responsive to signals from the sensor forcontrolling the movement of a loading coil in the antenna to place theantenna in resonance with the RF signal.

This invention relates to antennas and antenna systems, and moreparticularly it relates to antennas and antenna systems transmitting andreceiving radio signals which incorporate adjustable inductance devicesfor tuning the antennas and antenna systems.

This invention is particularly useful where a single antenna system isused over a wide frequency range by unskilled personnel, and the antennais located remotely from the transmitter or receiver.

The strength of the electromagnetic field radiated from a section ofwire carrying radio frequency current primarily depends on the length ofwire and the amount of current flowing. Other things being equal, thefield strength is directly proportional to the current flowing. Hence,it is desirable to :make the current flowing as large as possibleconsidering the power available. It is well-known that the powerradiated by an antenna operated at resonance is substantially increasedover one not operated at resonance for a given power availability at atransmitter, and similarly the receptivity of a resonant antenna inreceiving radio energy is increased.

In practice, especially in mobile work, it is often necessary to providea single antenna, usually of fixed small physical length, which iscapable of satisfactory operation over a broad band of frequencies. Theantenna operates in such a manner that its impedance match with atransmission line at each of the frequencies is satisfactory foroperability. This type of operation and construction is used often inaircraft, automotive vehicles, trucks, small boats or other movingconveyances, where for reasons of economy of space and weight, a singleantenna system must be use-d.

In many instances these antennas of fixed length have a maximumdimension, which is small compared to the operating wave length, andhave impedance characteristics which vary rapidly with frequency. Goodoperation is normally only achieved over a relatively narrow range offrequencies, if fixed matching networks and tuning elements are used.For use over a range of frequencies, these antennas require retuning ofthe matching circuit of the antenna system as the frequency of operationis changed.

The industry has long recognized the advantages of being able to exactlyresonate an antenna to any frequency quickly over a certain range, andmany attempts have been made to solve this problem. Antennas have beenremotely tuned by switchable lumped reactances, sliding tappedinductions and physically changing the length of the antenna. Whilethese methods have improved the matching and tuning, they have notsolved the problem.

These advantages are especially significant for mobile operation inwhich physical limitations ordinarily require antenna length to besmaller than a quarter wave length "ice of the wave length of theexciting energy. Also, mobile operation incurs constant change ofenvironment, which continually changes the resonant characteristics ofthe antenna, and operation by relatively unskilled personnel.

One of the objects of this invention therefore is to provide an antennacapable of being automatically resonated over a band of frequencies.

Another object of the present invention is to provide an antenna systemhaving a higher radiating efiiciency over :a wide band of frequency.

A further object of the present invention is to provide a single antennacapable of having its effective electrical length quickly and easilyvaried to offer maximum effectiveness for radiation of energy at two ormore frequencies, without requiring a complex tuning or matching networkto maintain a constant input impedance characteristic.

Another object is to provide an antenna system which can be adjusted foroperation with a variety of transmitters and receivers operating at thesame or different frequencies and which may be adjusted for operationremotely.

Still another object of the present invention is to provide an antennasystem, which can be electrically changed to adapt to physical changesin environment and which automatically prevents damage to the equipmentregardless of careless operation by the operator.

A still further object of the present invention is to provide an antennasystem of relatively constant physical length, which may be maderesonant automatically covering a range of frequencies and which isrelatively simple and rugged in construction and is small and compact insize.

Other objects, features and advantages of the invention will becomeapparent upon reading the following description, taken in conjunctionwith the accompanying drawings, in which:

FIGURE 1 is a block diagram showing an antenna system in accordance withthe present invention remotely coupled to a transmitter and receiver,which may operate on different frequencies;

FIGURE 2 is a schematic diagram of a circuit of the present inventionfordetecting whether an antenna is resonant or non-resonant with respectto a given signal;

FIGURE 2A is a modification of a portion of the circuit of FIGURE 2;

FIGURE 3 is a schematic diagram of a circuit in accordance with thepresent invention for automatically tuning the antenna duringtransmission;

FIGURE 4 shows a cross-sectional, side-elevational view of a variablereactance in accordance with the present invention;

FIGURE 5 is a cross-sectional view taken 5-5 of FIGURE 4;

FIGURE 6 is a cross-sectional view of the variable inductance takenalong line 6-6 of FIGURE 4; and

FIGURE 7 is a schematic diagram of circuits for switching a receivingunit into and out of the antenna circuit.

Referring now to the drawings, FIGURE 1 diagrammatically shows atransmitting-receiving system in which radio signals from a transmittingand/or receiving apparatus 10, illustrated as a radio-telephone, areradiated or received by a remotely positioned antenna 12. Remotelypositioned refers to a distance of about six feet or more. The followingdescription will discuss the operation of the system for transmissionuntil otherwise specified. The signals are fed from transmitter 10 tothe antenna structure 12 through transmission lines or cables 14, whichmay be coaxial cables. The receiver, also designated as 19, may beoperated on a frequency different from that used by the transmitter.

along line Antenna 12 is shown as being made up of a plurality ofelongated, electrically conductive sections, which are designated as abase section or radiator 16 and an upper section or radiator 18.Additionally, as discussed below, interconnecting a resonance detectorunit 28 and a receiver matching and switching unit 24 is an antennasection 19. q I

Physically interposed between antenna base portion 16 and antenna upperportion 18 is a variable reactance as sembly 20, which, as explained indetail below, includes an inductive element or loading coil connected inseries with antenna sections 16 and 18. Antenna 12, also ilIustrativelyshown, has a capacitive top loading element 2 which as illustrated,takes the form of a disc and is used for improving efiiciency, andallowing antenna 12 to be resonated with less loading inductance andtherefore less losses. The design of capacitive loading element 22should be such as to otfer the maximum capacity that is mechanicallypossible and not present a shorted conductive path to any of themagnetic flux generated by the loading coil in variable reactanceassembly 20.

During transmission, a radio signal from radio-telephone unit is carriedby transmission line 14, which is preferably a coaxial line.Transmission line 14 is interconnecting radio-telephone unit 10 and a.receiver matching and switching unit 24. Interconnected in line 14 is aswitch or relay 15, one section of which in its 1 closed positionbypasses unit 24 via transmission line 27, when relay is energized by asignal from radio-telephone unit 10 during transmission. The transmittedsignal is fed directly into antenna section 19 via transmission line 27and into lower radiator 16 via resonance detector unit 28. If antenna 12is not at resonance with the frequency of the transmitted signal, asuitable load impedance 158, which, as shown, is in programmer unit 30,is placed in the output line. via conductor 32. Since antenna 12 isnormally initially detuned, it is not accepting any radio signals fromtransmitter 10 and dummy load impedance 158 in the output circuitprevents the output amplifier tubes and their modulator of transmitter10 from exceeding their normal dissipation. In a manner as will bediscussed hereinafter, resonance detector unit 28 detects that antenna.12 is not properly tuned and signals an amplifier circuit 34 viaconductor 36. Preferably, amplifier circuit 34 comprises dual circuits,which are not shown. The signal transmitted by resonance detector unit28 to amplifier circuit 34 varies in polarity in response to whether thetuning frequency of the antenna is above or below the freqency of thetransmitted signal. For example, the signal transmitted from resonancedetector unit 28 to amplifier circuit 34 can be made positive, ifantenna 12 is tuned to a frequency above the exciting transmitted radiofrequency and negative if the tuned frequency is below the frequency ofthe exciting transmitted radiov frequency. Amplifier circuit 34 isnorm-ally in an ON condition and sending a signal, or signals where dualcircuits are utilized, to programmer unit via conductors 37 foradjusting the resonant frequency of antenna 12.,When amplifier circuit34 receives a signal of different polarity from resonance detector unit28, amplifier circuit 34 signals programmer unit 30 via conductor 37,which varies the resonant frequency of antenna 12, as discussedhereinafter. Depending upon the signal received by programmer unit 30from amplifier circuit 34, the direction of rotation of motor 38 iscontrolled to vary the inductance of reactance assembly 20, so as totune antenna 1'2 towards resonance at the frequency of the transmittingsignal. As antenna 12 approaches resonance, it begins to accept theradio frequency energy from transmitter 10. The acceptance of thetransmitted signal by antenna 12 is also sensed by resonance detectorunit 28, which signals programmer unit 30 via dual amplifier circuit 34for removing the dummy load from line 32 and also begins the process tostop motor 38. Various'modes of pragramming can be used to une antenna12 an 4 maintain antenna 12 in tune, which will be discussed hereinafter. Advan'tageously, when antenna 12 is in tune, the operator issignalled in some manner, such as illuminating a signal light 40 toprovide a simple visual indication to the operator, when antenna 12 isaccepting maximum power. Of course, other signaling devices, such as abuzzer, could be used.

In order to prevent damage to the mechanism of the variable reactanceassembly 20, some type of limit control must be utilized, whichautomatically triggers programmer unit 30 via line 42 to reverse thedirection of motor 38.

If the frequency of the received signal differs from the frequency ofthe transmitted signal, the impedance of the received signals must beadjusted to the cable impedance to avoid attenuation. As shown in FIGURE1, a separate receiver switching and matching unit 24 is used, which isremotely adjusted by unit 25.

As shown in FIGURE 7, receiver switching and matching unit 24 is in theantenna circuit only during reception. Relay switch 15 connects orbypasses unit 24 in accordance with signals received by coil 26. Antennasection 19 is coupled into a parallel-tuned tank circuit 242 via acoupling capacitor 224. The resonant frequency of tank circuit 242 isadjusted by means of a saturable reactor 246. The reactance of reactor246 is remotely controlled by a tuning current in a coil 248, whichcurrent is adjusted by a pot 250. Transmission line 14 is coupled intotank circuit 242 by a link 253. The ratio of the turns of link 253 tothe turns on the saturable reactor 246 is adjusted to give the bestmatch over the band of frequencies to be covered.

During transmit operation, the separate, remotely controlled receiverswitching and matching unit 24 is switched out of the antenna circuit byswitch 15 being open when coil 26 is energized. The transmitted signalbypasses receiver switching and matching unit 24 and is fed directlyinto antenna section 19. For receive operation, the operator sets thereceiver of the radio-telephone 10 to the desired frequency, and thenadjusts pot 250 in the receiver matching control network 25 for maximumsignal.

FIGURES 4, 5, and 6 show the details of variable re- 7 actanceassembly20. The lower end of upper radiator 18 is fixedly mounted to oneend of variable reactance assembly 20. Similarly, the upper end of lowerradiator 16 of antenna 12 is fixedly mounted to the other end ofvariable rectance assembly 20. Variable reactance assembly 20 comprisesan elongated hollow coil form 52, preferably cylindrical in form, formedof insulating material and having a central passage 54 therethrough. Atopposite ends of form 52 are end pieces 56 and 58 positionedtransversely across passage 54. End piece 56 has a tapped opening 60 forattachment of the upper radiator 18, which has a cooperatively threadedstud for mating with threaded opening 60. Similarly, the top end of thelower or base radiator 16 is received within the corresponding end 58 oftubular form 52 in any convenient manner. Advantageously, base radiator16 is hollow.

. Mounted about coil form 52 is a coil '50. Coil Stl'is advantageously acontinuous conductor or a number of conductors connected in series,which is wound in either a single ora multiple layer formation in aconventional manner. Proper selection of the wire size and the number ofturns per inch in the helix and the manner of winding will reduce thelosses caused by eddy currents formed in the individual turns of thecoil 50, as well as lower the capacitive coupling between adjacentturns. Coil 50 is electrically connected to the base section radiator 16by means of a conductor .62, which is shown electrically connecting baseradiator 16 by means of a screw 64. Similarly, coil 50 is electricallyconnected to the upper radiator by means of a conductor 66, which isconnected to upper radiator 18 by a screw 68.

To increase the inductance of coil 50, a core of high permeabilitymaterial is disposed within passage 54 and within and adjacent coil 50.To cover a wide range of power output transmitters, a series of spacedapart rods 70 is distributed about the inner diameter of coil 50, asseen best in FIGURES 5 and 6. For obtaining sufiieient reactance change,a hi h permeability material is used, such as a ferromagnetic ceramicmaterial, such as described by Snoeck in US. Patents 2,452,529,2,452,530 and 2,452,531. This material maintains a high Q even whensubjected to substantial magnetic saturation and also provides a widerange of inductance variation. To prevent individual rods 70 from beingoverheated at higher radio frequency power input into coil 50, it isnecessary to place a shield about each of the rods to insure that themagnetic flux from coil 56 is evenly distributed between the severalrods 70. In place of the individual shields about each of the rods, anelectrically conductive member 72 mounted along the axis of symmetry ofthe rods 70 provides suflicient shielding to promote even distributionof the magnetic flux to the various rods 70 and thereby eliminating rodhot spots and lossess. Conductive member 72 may be made of brass,aluminum, copper and can. also be silverplated.

To vary the inductance of coil 50, rods '70 are withdrawn or introducedinto coil 50 at a desired rate. It is observed that withdrawing orintroducing rods 70 into coil 50 a predetermined amount, resonatesantenna 12 for operation at the desired frequency. Therefore, thepreselected introduction or withdrawing of rods '70 permits quick andsimple adjustment of the reactance of coil 50, which varies theresonance of antenna 12 over a variety of frequency ranges.

Conductive member 72 is shown in the form of a cylinder and is threadedas seen best in FIGURE 4, and as discussed below operates as a shaft.End piece 56 of coil form 52 has an interiorly directed, centrallydisposed opening 74 for rotatably receiving a reduced diameter end ofmember 72. Mounted within coil form 52 and adjacent the upper end oflower radiator 16 is reversible motor 38 with a suitable gear train forsecuring the desired output speed of rotation. Motor 38 and its geartrain are shown as a single unit and are fixedly mounted within tubularform 52 in any convenient manner, such as shown by a bolt and nut 78.Advantageously, motor 38 is reversible and has its output shaft 80rotate at a fixed speed determined by the gear train. Output shaft 80 iscoupled to the upper end of member '72 by means of an insulated coupling82. Rods 70 are mounted in any convenient manner on two end plates 84and 86, which are made of insulated material. As shown, the ends of rods70 are reduced in diameter and fitted into openings in the respectiveend plates 84 and 86. Attached to one of the rod end plates,illustratively shown as attached to end plate 86, is a threaded bushing88. Threaded bushing 88 cooperatively engages threaded member 72 formoving rods 70 and end plates 84 and 86 in unison longitudinally alongthe interior of coil form 52. EX- tending through tubular form 52 andbetween adjoining rods 70 are a plurality of stop fingers,illustratively shown as three in number, 90, 92 and 94. Fingers 9t), 92,and 4 prevent the rod assembly from rotating during longitudinalmovement within passage 54. Hence, when motor 38 rotates threaded member72 in one direction, rods 79 move into coil 50 and when motor 33 rotatesin the opposite direction, rods 76 are Withdrawn from coil 59. Fingers90, 92 and 94 also limit the length of longitudinal movement of theassembly of rods 70 to prevent damage by the movement of the assembly ofrods 70 exceeding the length of coil form 52. As shown in FIGURE 4,attached to the interior surface of end plate 86 is a conductive sheet96, which is positioned to have portions 96a and 96b engage fingers 92and 94, respectively, when fully traversed, so that rods 70 are fullyinserted within coil 54 as shown in FIGURE 4. Fingers 92 and 94 areelectrically connected by means of sheet 96. Similarly, attached to theinterior surface of end plate 84 is a conductive sheet 98, which ispositioned to have portions 98:: and 98b contact fingers and 92,respectively, when the assembly of rods 70 is fully traversed to theleft, as shown in FIGURE 4. Fingers 90 and 92 are electrically connectedby means of electrical conductive sheet 98. Advantageously, theelectrical conductors 91, 224 and 230 for fingers 90, 92 and 94,respectively, and electrical conductors 164 and 166 for motor 38, arecarried within the interior of antenna section 16. When correspondingfingers 90, 92 and 94 make contact with their corresponding conductivesheets 96 or 98, a signal is sent to reverse direction of motor 38 in amanner which will be discussed below.

The schematic circuit diagram of the resonance detector unit 28 is shownin FIGURE 2. Resonance detector unit 28 signals when antenna 12 is incondition to accept efiiciently the radio frequency signal. Antenna 12is both transformer and capacity-coupled to resonance detector unit 28.The primary coil 100 of the RJF. transformer is coupled to antenna 12and the R.F. source from radio-telephone 10. Primary coil 100 is coupledto two transformer secondary windings 102 and 104. The circuit composedof coils 10! and 10-2, and resistors 105, 106 and 130, capacitors 108,iii), 1 12, 114, 116 and 118, and diodes 120 and 124, and choke coils126 and 12 8, form a conventional phase detector circuit with RF.current filtering in the output circuit. This circuit is hereinafterdesignated as resistive load detector circuit 119. An LC. filter iscomposed of capacitors 116 and 1-18 and coil d28. When antenna 12 isresistive and drawing current, the output across capacitor 116 will be0. Capacitors 1% and 11% form a capacitive network divider and feedcapacitively coup-led RF. voltage to the resistor-diode network formedof resistors 105 and 106 and diodes 129, and 124, to provide a voltagein phase with the antenna R.'F. voltage. Depending upon the polarity ofcoil 100 with respect to coil 162, the voltage across capacitor 116 willbe of one polarity when antenna 12 has a capacitive reactance (i.e., theantenna is tuned to a frequency above the exciting radio frequency) andthe polarity of the voltage will be reversed when antenna 12 has aninductive reactan-ce (i.e., the antenna is tuned below the excitingradio frequency).

Resistor 130 has an adjustable tap which is used to offset the null orzero output in the LC. output filter shown, so that the system ceases totune when antenna 12 is accepting maximum power.

The circuit shown in FIGURE 2 composed of coil 100 and coil 14M, diode134, capacitor 136 and resistor 138, produces a positive output voltagesignal when RF. current is accepted by antenna 12 through coil 100. Thiscircuit is hereinafter designated current detector circuit 135. Theoutput signals of resonance detector unit 28 are coupled to amplifierunit 34 via conductors 36a and 36b. Conductors 36a and 3612 may each beconnected to a separate amplifier circuit.

Amplifier unit 34 is a conventional D.C. amplifier, and is preferably atransistorized DC amplifier, such as found in the Transistor Manual,sixth edition, published by General Electric Company; RCA TransistorManual, Technical Series SC-10; and Silicon Zener Diode and RectifierHandbook, second edition, published by Motorola, Inc. Amplifier unit 34amplifies the output signals of resonance detector unit 28 received viaconductor-s 36a and 36b, and feeds these amplified signals intoprogrammer unit 3%.

The schematic wiring diagram of programmer unit 30 is shown in FIGURE 3.Programmer unit 30 is electrically coupled to amplifier unit 34,resonance detector unit 28 and the limit switch assembly of control rods70, as shown in FIGURE 4. As shown in FIGURE 3, programmer unit 3%contains four relays, 150, 152, 154 and 156, which advantageously eachis a double-pole, double-throw type, and is shown in its unenergizedstate. Relay operates to control the direction of rotation of motor 3 8,which controls the position of rods '70 in variable reactance assembly20. Once relay 159 is energized, it remains energized for as long as thetransmit signal from radiotelephone unit 10 continues or until relay 154is energized.

Relay 152 operates to turn off the tuning motor 38. Relay 152 iscontrolled by the output signal of amplifier unit 34, which in turnreceives a signal from resonance detector 28 when antenna 12 isresistive, or is tuned to the transmitted signal. When relay 152 isenergized, it forces relay 150 to latch, unless relay 154 is energizedor closed.

Relay 154 is used to unlatch relay 15d and thereby reverse the directionof rotation of tuning motor 38 when the appropriate limit switch contact93 is made with corresponding fingers 90 and 92. Relay 154 remainsenergized for as long as relay 152 is energized.

Relay 156 operates to prevent relay 152 from shutting off tuning motor38 unless relay 156 is deenergized. Relay 156 also places a dummy load,shown as resistor 158, across the RF. output line to protect thetransmitter during tune-up of antenna 12 and releases the dummy loadresistor 158 when deenergized. Relay 156 is normally energized by anoutput signal from dual amplifier unit 34, which in turn receives anoutput signal from resonance detector unit 28 when antenna 12 beginsdrawing current. When antenna 12 begins drawing current, amplifiercircuit 34 signals relay 156 to shut off so as to remove the dummy loadresistor 158 from the R.F. output circuit and allows relay 152 to shutoff the tuning motor 38.

Diode 160 is interposed between conductor 166 and contact 179 of relay152 to give tuning motor 38 dynamic braking when it is shut ofl by relay152. Diode 162 prevents momentary shorting of the supply energizingcurrent when relay 150 is being energized by the closure of relay 152.Indicator 40 is energized when relay 151i is energized and relay 152 isdeenergized, which indicates the tune-up of antenna 12.

Motor 38 is electrically connected to programmer unit 30 by conductors164 and 166, which are carried within lower radiator 16, as shown inFIGURE 4. When both relay 150 and relay 152 are energized, motor 38receives a signal via conductors 164 and 166, so as to rotate member 72in a direction to withdraw rods 70 from within the reactance coil 50 andthereby raise the resonant frequency of antenna 12.

Generally the operation of the antenna system of the present inventionis as follows:

Prior to the antenna system of the present invention, receiving aninitial signal from radio-telephone unit 10, relays 150, 152, 154 and156 in programmer unit 39 are in their unenergized condition, as shownin FIGURE 3. An initial signal from radio-telephone unit 10 is sent toprogrammer unit 31 via conductor line 13. Advantageously, this signal isa D.C. signal, which is readily available during the transmit cycle ofradio-telephone unit 10. When this initial signal is received byprogrammer unit 30, relay 156' is unlatched and tuning motor 38 of thevariable reactance assembly begins rotation in a direction to introducetuning rods 70 into coil 50 for lowering the resonance of antenna 12.However, simultaneously amplifier unit 34 is actuated by this initialsignal via line 13, and energizes relays 152 and 156 via conductors 37.Signals from amplifier unit 34 via conductors 37 energizes coil 178 ofrelay 152, thereby closing contacts 180 and 182. Similarly, amplifierunit 34 energizes coil 186 of relay 156 via line 37 and closes contacts188 and 190.

When relay 152 is closed, contact 182 is closed, which energizes coil192 of relay 150 for completing the circuit via contact 210 of relay 154and conductor 220, thereby closing relay 150, which closes contacts 194and 196. Closing of relay 150 reverses the polarity of the voltageapplied to motor 38 via conductors 164 and 166, and thereby reversingits direction and causing variable reactance assembly 20 to tune theantenna upward in frequency. When relay 150 is deenergized and aninitial D.C.

signal is applied via conductor line 13-, conductor 164 to motor 38, isnegative as shown and conductor 166 is positive as shown. Energizingrelay 150 closes contact 194 making conductor 166 negative and closescontact 196 making conductor 164 positive via conductors 198 and 2134,through contact 158 of relay 156 to conductor 200. Since relay 156 isenergized by the output of amplifier unit 34, dummy load resistor 158 isin the RP. output circuit via transmission line 32 and contact 191).Contacts 194 and 196 of relay 159 are connected when relay 156 isenergized in the manner described above with respect to making conductor164 positive.

Relay 150 remains latched while relay 152 is energized, since thecircuit of coil 192 of relay 150 is completed from line 13 through coil192 via conductor 263 through contact 210 of relay 154, via conductor22% through contact 132 of relay 152 to the opposite polarity. Withrelay 150 latched, motor 33 continues to rotate in the same directionuntil control rods 71 are fully withdrawn. When control rod assembly '72is fully withdrawn from coil 50, conductive sheet 98 on end plate 84makes contact with fingers 9t) and 92. Finger 92, as shown in FIGURE 3,is connected to negative potential via line 224, which grounds finger9%. Finger 9%) is connected to coil 226 of relay 154 for completing thecircuit of coil 226 and thereby energizing coil 226 and closing relay154. When relay 154 closes, it deenergizes relay 159 by breaking ofcontact 219. When relay 159 is deenergized, the polarity of motor 33 isreversed, causing motor 33 to reverse direction and introduce slugassembly 70 into coil 59. Coil 226 of relay 154 continues to beenergized and thereby relay 154 is closed through contact 216 of relay154, via conductors 228 and 294, through contact 188 of relay 156, viaconductors 20% and 163, through contact 193 of relay 150 to negative.Motor 38 will continue to rotate in this direction until control rods 70are fully within coil 50 and sheet 96 makes contact with fingers 92 and94, as shown in FIGURE 5. When this occurs, finger 94 is grounded andcompletes the circuit of coil 192 of relay 150 via conductor 208 forcausing a current to pass through coil 192 and thereby energize relay150, which changes the polarity supplied to motor 38 via conductors 164and 166, which reverses the direction of rotation of motor 38 forwithdrawing control rods 70 from coil 50. The closing of relay 159breaks contact 193 which in turn breaks the circuit of coil 226, whichunlatches relay 154.

Control rods 70 continue to oscillate between sheets 96 and 98 until anR.F. signal is received.

When a radio frequency signal, higher in frequency than the antennaresonant frequency, is attempted to be transmitted via antenna 12,antenna 12 appears as an inductive load to resonance detector unit 28.The output across capacitor 116 of the phase detector circuit ofresonance detector unit 28 is negative and since there is no antennacurrent, the output from the current detector circuit of resonancedetector unit 28 is O. A zero current and a negative phase signal outputfrom resonance detector unit 25 causes amplifier 34 to conduct, andprogrammer unit 30 is actuated in a manner similar to that describedabove, with no RF. signal applied. The initial actuating signal fromradio-telephone unit 10 via line 13 energizes relay and the outputs ofamplifier 34 energize relays 152 and 156. With the relays in thiscondition, motor 38 is rotated in a direction to remove control rods 76from coil 50, which raises the resonant frequency of antenna 12. As theresonant frequency of antenna 12 approaches the frequency of the RF.signal, antenna 12 begins drawing current. Current flowing in antenna 12causes the current detector circuit 135 of resonance detector unit 28 totransmit a positive signal to the circuit of amplifier 34 coupled tocoil 186 of relay 156, which breaks the output signal from an plifier 34and deenergizes relay 156, The opening of relay 156 removes dummy loadresistor 158 from the RF. output conductor 32 allowing radio-telephoneunit to apply full power output to antenna 12. Further, the opening ofrelay 156 places relay 152 in condition to stop motor 38. Motor 38continues to rotate in the same direction even when relay 156 opens. Asthe resonant frequency of antenna 12 increases, the output signal ofresistive-load detector circuit 119 of resonance detector unit 28becomes less negative in phase and then becomes positive. A positivesignal received by amplifier 34 from the resistive load detector circuit119 of resonance detector unit 28 cuts off the output signal ofamplifier 34 applied to relay 152 and thereby deenergizes coil 178 ofrelay 152. The opening of relay 152 turns off motor 38 by breakingcontact 180 of relay 152 and places dynamic braking diode 160 acrossmotor 38 through contact 179. Simultaneously, indicator is energized byreason of contact 181 of relay 152. In the present operation of thisunit, relays 152, 154 and 156 are deenergized and only relay 150 remainsenergized. As discussed above, variable resistor 138 of resonancedetector unit 28 is adjusted so that motor 38 and control rods stop whenantenna 12 is accepting maximum power.

When a radio frequency signal having a lower frequency than the resonantfrequency of antenna 12 is transmitted by radio-telephone unit 10 and aninitial signal is applied via line 13, antenna 12 appears as acapacitive load to resonance detector unit 28. The output of theresistive load detector circuit 119 of resonance detector unit 28 ispositive. Applying the positive signal from resistive load detectorcircuit 119 to amplifier 34 via conductor 36a, breaks the output signalof amplifier 34 coupled to coil 178 of relay 152 of programmer unit 30.No current flows in antenna 12 so the current detector circuit is zero.Amplifier 34 receiving no signal from current detector circuit 135 sendsa signal to coil 186 of relay 156. Thus, relays 150, 152 and 154 ofprogrammer unit 38 remain open. Since relay 156 is energized, dummy loadresistor 158 is placed in the output circuit of radio-telephone unit 10.The polarity of the signal applied to motor 38 directs control rods 70into reactance coil 58, which decreases the resonant frequency ofantenna 12. As the resonant frequency of antenna 12 approaches that ofthe frequency of the transmitting signal, antenna 12 begins to acceptcurrent, which causes current detector circuit 135 of resonance detectorunit 28 to transmit a positive signal to amplifier unit 34 via conductor36b, which cuts off the signal from amplifier unit 34 to coil 186 ofrelay 156, thereby deenergizing coil 186. Opening of relay 156 removesdummy load resistor 158 from the RF output line, which allows antenna 12to receive all of the output signal from radiotelephone unit 10 andgives control to relay 152 to shut off motor 38. As the resonantfrequency of antenna 12 is reduced, it becomes closer to the frequencyof the transmitted signal, causing the phase of the output signal of theresistive load detector circuit 119 of resonance detector unit 28 tobecome less positive until the output signal ceases to be positive andbecomes essentially zero, when the resonant frequency of antenna 12 isequal to the frequency of the transmitted signal. When the output signalfrom resistive load detector circuit 119 is essentially zero, a circuitin amplifier unit 34 coupled to coil 178 of relay 152 is biased on andbegins to conduct and thereby energizing coil 178 of relay 152 andclosing relay 152. As discussed in the above examples, relay is thenlatched and the sequence described above occurs.

If for any reason the transmission of the R.F. signal ceases, and thencontinued on the same frequency, none of relays 150, 1-52, 154 and 156close, causing motor 38 to tune antenna 12 to lower frequencies. Theprocedures described above occur, which causes a recycling of resonantfrequency of antenna 12 until the right frequency is obtained.

If diode in the circuit of programmer unit 30, shown in FIGURE 3, isdisconnected, and a connection is made between contact 1 80 of relay 152and contact 216 of relay 154, shown by dashed line 234, a continualsensing of the resonant frequency of antenna 12 is provided, so that theresonant frequency of antenna 12 is corrected throughout thetransmission of an R.F. signal from radio-telephone unit 10. Operationis similar to that described above, except motor 38 is not cut off asdescribed above at the tuned frequency. Instead of motor 38 being cutoff when relay 152 is deenergizcd, conductor 234 connecting contact ofrelay 152 to contact 21-6 of relay 154 grounds relay 154 causing it toclose. The closing of relay 154 unlatches relay 150 making tuning motor38 lower or reduce the resonant frequency of antenna 12. This reductionin the resonant antenna frequency continues until the resistive loaddetector circuit 119 of resonance detector unit 28 produces a signal toclose relay 152, which in turn closes relay 150 and releases relay 154,so that a signal is transmitted to motor 38 reversing its direction soas to tune the resonant frequency of antenna 12 upward in frequencyuntil relay 152 opens, and the process is repeated.

If the antenna 12 is close to the radio-telephone unit 10, i.e., about 6feet, it is sometimes desirable to elimimate a non-radiatingtransmission line altogether. In this case receiver matching andswitching unit 24, relay 15, transmission line 14 and bypass line 27 iseliminated and horizontal antenna section 19 will go directly to theradiotelephone unit 10. This approach has application in marine mobileoperations, and eliminate the problem of antenna matching and tuningwhen both identical and different frequencies are used for transmissionand reception. It a low impedance transmission line, such as coaxialcable, is used between resonance detector unit 28 and radio-telephoneunit 10, and the same frequency for transmitting and receiving is used,antenna 12 can be tuned for both receiving and transmission bytransmitting a signal. With these requirements, receiver matching andswitching unit 24 and receiver matching control unit 25 can beeliminated and horizontal antenna section 19 will connect directly toradio-telephone unit 10 via transmission line 14. However, thisprocedure requires the transmission of a signal, so as to properly tunethe set both for transmission and receiving.

Occasionally, where the resonance detector unit 28 is located remotefrom the variable reactance assembly 28, stray capacitance of theantenna circuit "becomes appreciable. This occurs when the physicaldimensions of the antenna is large. If the stray capacitive reactance inthe antenna circuit is appreciable to resonance detector unit 28, theresonance detector unit 28 will be actuated in the same sense that itwould be when the radio frequency signal being transmitted is at a lowerfrequency than the antenna resonant frequency. In this situation antenna2 may be unintentionally tuned away from the frequency of thetransmitted signal. This normally is not critical, since control rods 70move in and out of coil 50 until an end stop conducting sheet 96 or 98contacts fingers 92 and 94, or 99 and 92, respectively, for reversingthe direction of movement of control rods 70, which movement continuesuntil the resonance frequency of antenna 12 matches the transmit orreceive frequency.

To avoid this occasional problem, a corrective circuit is shown inFIGURE 2A, where a coil 238 is added to primary coil 108 of resonancedetector unit 28. Coil 238 is identical to primary coil 108 andconnected so that its polarity is opposite and equal to the polarityacross coil 100. Coil 238 is coupled to a variable capacitor 240 andthrough relay 156a to ground, when switch a of relay 156a makesconnection with contact a, which occurs when coil 186a is energized in amanner similar to coil 186 of relay 156. Since, as shown in FIGURE 3,dummy load resistor 158 is coupled to switch 185 of relay 156, a dummyload resistor 158a is added to relay to the stray capacity of theantenna circuit, so as to cancel the effect of the stray capacitance inthe circuit, insofar as the resonance detector unit 28 is concerned.When the current detector circuit 135 of the resonance detector unit 28senses that antenna 12 is drawing current, coil 186a is deenergizedwhich removes dummy load resistor 158a from the RF. output circuit, inthe same manner as described above.

While the control rods 70 were shown to be fully within coil 50 in theirmaximum IN position, if desired, coil t) can be lengthened, so as to belonger than the maximum inward position of the control rods 70. Thiswill provide a more restricted frequency band than described above, withless stray capacity introduced into coil 50 0t FIGURE 4.

Further, while a plurality of control rods 79 were shown, a solid slugor tube may be used. However, because of the range of power intended tobe handled by the present invention, the use of a plurality of rodsprovides more flexibility. With the larger power RF. outputs, the use ofrods materially decreases the weight and cost of the variable reactanceassembly as compared to the use of a solid or cylindrical core.

In the various arrangements shown, additional circuit elements may beused where required. For example, to transfer the receiving energy fromthe antenna to the receiver, various approaches may be used. A saturablereactor in series with the center portion of antenna 12 could beswitched into the circuit on receive, which reactance can be remotelycontrolled by a tuning circuit, which can be adjusted by the variableresistor 130 of the resonance detector circuit 28 shown in FIGURE 2.Additionally, the energy from antenna 12 is coupled to the transmissionline to the receiver by means of a parallel tuned tank through acoupling capacitor. The resonant frequency of this tank can be adjustedby means of a saturable reactor, similar to that mentioned above. Thetransmission line is coupled into the tank circuit by means of a linkwhich can be varied to the turns of the tank to provide the best matchover the band of frequencies contemplated. Various alternative elements,such as a broadband matching transformer, can be coupled into thesecircuits to provide the necessary impedance matching.

While the apparatus of the present invention was shown varying theinductance of the antenna, similar apparatus can be used to varycapamtive reactance. If a variable capacitor were substituted for thevariable inductor illustrated, and it were coupled to the antennasections, the reactance of the antenna would also vary. This would bereadily available if the antenna were made inductive so that varyingcapacitance would change the reactance.

Further, the antenna was shown vertically oriented, but could behorizontally oriented as well.

Also, the flux shield or flux equalizer 72 was shown mounted coaxiallywithin coil 50. However, shield 72 could be offset sometimes from thecoil axis and perform satisfactorily.

Various remotely controllable antenna tuning systems have been describedand from this description it would be apparent that antenna tuningsystems embodying the present invention are well-adapted to attain theends and ob- 'ects set forth herein and that the various embodiments ofthe invention shown herein can be modified so as to produce operatingcharacteristics best suited to the needs of each particular use.

While the principles of this invention have been described with respectto specific embodiments, it is to be understood that this description ismade only by way of example and not as a limitation to the scope of theinvention as set forth in the objects thereof and in the accompanyingclaims.

What is claimed is:

1. An antenna system tunable over a broad range of frequencies for usewith a source of RF energy, comprising an antenna having at least afirst and a second conductive section, a variable reactance memberinterposed between and coupled to said first and second sections, saidantenna having its electrical length changeable in response to varyingthe reactance of said reactance member, means coupling said RF source tosaid antenna, means coupled to said antenna for detecting resonance ofsaid antenna with said RF source, said detecting means couplingcontaining stray capacitance, means producing a counter reactance tosaid stray capacitance, said counter reactance coupled to said detectingmeans, so that said detecting means is substantially responsive only toantenna reactance, and means responsive to said detector means forvarying the reactance of said reactance memher to change the electricallength of said antenna so as to tune said antenna to receive maximum RFpower from said RF source.

2. An antenna system tunable over a broad range of frequencies for usewith a source of RF energy, comprising a antenna having at least a firstand a second conductive section, a variable reactance, member interposedbetween and coupled to said first and second sections, said antennahaving its electrical length changeable in response to varying thereactance of said reactance member, means coupling said RF source tosaid antenna, means coupled to said antenna detecting said antennabeginning to accept current from said RF source, said detector meansincluding means nullifying stray capacitance of said antenna conductivesections between said detecting means and said variable reactancemember, an RF power-absorbing load adapted to be coupled to said RFsource for receiving said RF energy, switching means adapted to coupleand uncouple said load to said RF source and said stray capacitancenullifying means, said switching means responsive to said detectingmeans for uncoupling said load and said stray capacitance nullityingmeans from said RF source when said antenna begins to accept currentfrom said RF source.

3. An antenna tuning system comprising an antenna unit having a firstand a second conductive section, a source of radio frequency energysignal for energizing said antenna, an energy transmission lineextending between said source and said antenna, and adjustable inductivereactance member interposed between and coupled to said sections of saidantenna, said inductive reactance member having a coil electricallycoupled to each of said antenna sections and a core of permeablematerial adapted to be moved into and out of said coil to vary theinductive reactance of said member, means for moving said core into andout of said coil for controlling the impedance relationship between saidantenna and said radio frequency signal, a detection unit coupled tosaid antenna for sensing the resonance of said antenna with said radiofrequency signal, switching means coupled to said detector unit foractuating said core moving means for moving said core with respect tosaid coil for varying the reactance of said reactance member to tunesaid antenna to the frequency of said radio frequency signal, and meansfor reversing direction of movement of said core automatically uponmovement of said core a predetermined distance.

4. An antenna tuning system comprising an antenna unit having a firstand a second conductive section, 'a source of RF energy coupled to saidantenna for energizing said antenna, an adjustable inductive reactancemember interposed between and coupled to said sections of said antenna,said inductive reactance having a coil electrically coupled to each ofsaid antenna sections and a plurality of spaced apart rods of permeablematerial adapted to be moved into and out of said coil for varying thereactance of said antenna, a member made of electrically conductivematerial coaxially aligned Within said coil, means coupled to said rodsfor moving said rods into received by said antenna from said RF source,switching means coupled to said detector unit for actuating said rodmoving means for moving said rods with respect to said coil for varyingthe reactance of said reactance member to tune said antenna to thefrequency of said RF signal,and means for reversing direction ofmovement of said rods automatically upon movement of said rods apredetermined distance.

5. An antenna tuning system comprising an antenna unit having aplurality of conductive sections, a source of radio frequency energyadapted to be coupled to said antenna for energizing said antenna, apower absorbing load coupled to said radio frequency source, anadjustable inductive reactance member interposed between and coupled toa pair of consecutive sections of said antenna, said inductive reactancehaving a coil electrically coupled to each of said pair of antennasections and a movable core of permeable material adapted to be movedinto and .out of said coil for altering the electrical length of saidantenna, means moving said core into and out of said coil, a detectionunit coupled to said antenna and adapted to send predetermined signalsin response to power received by said antenna, switching meansresponsive to signals from said detector unit for actuating said coremoving means for moving said core with respect to said coil and varyingthe reactance of said reactance member, second switching meansresponsive to signals from said detection unit for uncoupling said powerabsorbing load from said radio frequency source, and means for reversingdirection of said core moving means automatically upon predeterminedcore movement, said core being moved with respect to said coil untilsaid antenna is at resonance frequency.

6. An antenna tuning system comprising an antenna unit having aplurality of conductive sections, a source of radio frequency energyadapted to be coupled to said antenna for energizing said antenna, apower absorbing load coupled to said radio frequency source, anadjustable inductive reactance member interposed between and coupled toa pair of consecutive sections of said antenna, said inductive reactancehaving a coil electrically coupled to each of said pair of antennasections and a movable core of permeable material adapted to be movedinto and out of said coil for altering the electrical length of saidantenna, means moving said core into and out of said coil, a coilconnected to said antenna, a detection unit coupled to said coil andadapted to send predetermined signals in response to power received bysaid antenna, said detecting unit including a coil coupled to saidlastmentioned coil and having equal and opposite electricalcharacteristics thereto, said detecting coil coupled to a variablecapacitor for nullifying the effect of stray capacitance in said antennaconductive sections between said inductive member and said detectingunit, switching means responsive to signals from said detector unit foractuating said core moving means for moving said core with respect tosaid coil and varying the reactance of said reactance member, secondswitching means responsive to signals from said detection unit foruncoupling said power absorbing load from said radio frequency source,and means for reversing direction of said core moving meansautomatically upon predetermined core movement, said core being movedwith respect to said coil until said antenna is at resonance frequency.

7. An antenna tuning system comprising an antenna unit having at least apair of conductive sections, a source of RF energy for energizing saidantenna, a receiver of RF energy from said antenna, an energytransmission line connecting said antenna to said receiver, means forcoupling said RF source to said antenna, impedance matching meanscoupling said antenna and said receiver, first switching meansresponsive to a predetermined signal for connecting said receiver tosaid impedance matching means and disconnecting said receiver from saidimpedance matching means in response to cessation of said predeterminedsignal, an adjustable inductive reactance member interposed between andcoupled to said pair of sections of said antenna, said inductivereactance having a coil electrically coupled to each of said pair ofantenna sections and a movable core of permeable material adapted to bemoved into and out of said coil for varying the reactance of saidantenna, a member made of electrically conductive material coaxiallyaligned within said coil, means coupled to said core for moving saidcore into and out of said coil for controlling the impedancerelationship between said antenna and said RF source, detection meanscoupled to said antenna and adapted to sense the power received by saidantenna from said RF source, second switching means responsive to saiddetection means for actuating said core moving means for moving saidcore with respect to said coil for varying the reactance of saidreactance member to tune said antenna to the frequency of said RFsignal, and means for reversing direction of movement of said coreautomatically upon predetermined core movement.

8. An antenna system tunable over a broad range of frequencies for usewith a source of RF energy and a receiver of RF energy, comprising anantenna having at least a pair of conductive sections, a variablereactance member interposed between and coupled to said pair of antennasections, said antenna having its electrical length changeable inresponse to varying the reactance of said reactance member, meanscoupling said receiver of RF energy to said antenna, said meansincluding impedance matching means, said coupling means being adjustablefor providing maximum transfer of signal from said antenna to saidreceiver, switching means responsive to a predetermined signal from saidRF source for uncoupling said receiver impedance matching means fromsaid antenna and coupling said RF source to said antenna, means coupledto said antenna adapted to detect said antenna having a resistive loadso as to receive a maximum power from said RF source, said detectingmeans giving predetermined output signals in response to the resonancefrequency of said antenna being above or below said RF of said source,and means responsive to said signals of said detecting means for varyingthe reactance of said reactance member to change the electrical lengthof said antenna so as to tune said antenna to the frequency of said RFsource.

9. An antenna tuning system comprising an antenna unit having at least apair of conductive sections, a source of RF frequency coupled to saidantenna for energizing said antenna, a conductor wound in a coilinterposed between said pair of antenna sections and electricallycoupled to each, a threaded cylinder rotatably and coaxially mountedwithin said coil and made of electrically conductive material, aplurality of rods movable parallel to the axis of said coil and into andout of said coil, said rods being spaced apart and made of a permeablematerial, a pair of end plates each affixed to corresponding ends ofsaid rods, said rods and said pair of end plates forming an assembly,means carried by one of said end plates threadedly engaging saidthreaded cylinder so that rotation of said cylinder in one directionmoves said rod assembly logitudinally in one direction and reversingrotation of said cylinder reverses direction of said rod assembly, areversible electrical motor coupled to said threaded cylinder, aplurality of fingers generally radially disposed between said rods anintersecting the path of travel of said end plates, the axis of saidfingers lying in a plane transverse to the axis of travel of said rods,means carried by each of said end plates for electrically connecting apair of said fingers at the end of travel of said rod assembly,detecting means coupled to said antenna for sensing resonance in saidantenna and adapted to sense the power received by said antenna fromsaid RF source, switching means responsive to said detecting means forselectively actuating said motor for moving said rods in relation tosaid coil for adjusting the tuned frequency of said antenna towards thefrequency of said RF source, said switching means reversing thedirection of said motor in response to a pair of fingers beingelectrically connected by one of said means carried by one of said endplates.

10. An antenna tuning system comprising an antenna unit having an upperand a lower conductive section, a source of RF frequency coupled to saidantenna for energizing said antenna, a conductor wound in a coilinterposed between said upper and lower antenna sections andelectrically coupled to each, a threaded cylinder rotatably andcoaxially mounted within said coil and made of electrically conductivematerial, a plurality of rods movable parallel to the axis of said coiland into and out of said coil, said rods being spaced apart and made ofa permeable material, a pair of end plates each affixed to correspondingends of said rods, said rods and said pair of end plates forming anassembly, means carried by one of said end plates threadedly engagingsaid threaded cylinder so that rotation of said cylinder in onedirection moves said rod assembly longitudinally in one direction andreversing rotation of said cylinder reverses direction of said rodassembly, a reversible electrical motor coupled to said threadedcylinder, a plurality of fingers generally radially disposed betweensaid rods and intersecting the path of travel of said end plates, theaxis of said fingers lying in a plane transverse to the axis travel ofsaid rods, means carried by each of said end plates for electricallyconnecting a pair of said fingers at the end of travel of said rodassembly, detecting means coupled to said antenna for sensing resonanceof said antenna and adapted to sense the power received by said antennafrom said RF source, a RF power absorbing load coupled to said .RFsource for receiving said energy, switching means responsive to saiddetecting means for selectively actuating said motor for moving saidrods in relation to said coil for adjusting the tuned frequency of saidantenna towards the frequency of said RF source, andmaintaining saidrods in position with respect to said coil for maintaining said antennaat substantial resonance during transmission, said switching meansreversing the direction of said motor in response to a pair of fingersbeing electrically connected by one of said means carried by one of saidend plates, and second switching means adapted to couple and uncouplesaid power-absorbing load to said RF source, said second switching meansresponsive to said detecting means for uncoupling said power-absorbingload from said RF source when said antenna is accepting current fromsaid RF source.

11. A variable reactance assembly, comprising a hollow elongatedcylinder formed of an insulating material, a coilof wire woundcircumferentially on said cylinder, a plurality of rods made ofpermeable material spaced apart in predetermined relation within saidcylinder, a threaded cylinder made of electrically conductive materialrotatably and coaxially mounted within said cylinder, a pair of endplateseach afiixed to corresponding ends of said rods, means carried byone of said end plates threadably engaging said threaded cylinder, sothat rotation of said threaded cylinder moves said rods longitudinally,means carried by said cylinder for rotating said threaded cylinder inopposite directions, and means electrically coupled to saidlast-mentioned means for limiting longitudinal movement of said rods byreversing rotation of said means.

12. An antenna system tunable over a broad range of frequencies for usewith a source of RF energy, comprising an antenna having at least afirst and a second conductive section, 'a variablereactance memberinterposed between and coupled to said first and second sections, saidantenna having its electrical length changeable in response to varyingthe reactance of said reactance member, means coupling said RF source tosaid antenna, means coupled to said antenna detecting said antennaaccepting current from said RF source, means nullifying straycapacitance of said antenna conductive sections between said detectingmeans and said variable reactance member, an RF power-absorbing loadadapted to be coupled to said RF source for receiving said RF energy,switching means adapted to couple and uncouple said load to said RFsource, and said stray capacitance nullifying means, said switchingmeans responsive to said detecting means for uncoupling said load fromsaid RF source when said antenna accepts current from said RF source.

References Cited UNITED STATES PATENTS Clark 343-403 X EDI 'LIEBERMAN,Primary Examiner.

